A physical-quantity sensor capable of detecting a physical quantity, such as an angular velocity and an acceleration, has been used in a variety of technical fields such as detection of a camera shake of a digital camera, attitude control of a movable unit, such as airplanes, automobiles, robots, and vessels, missile guidance, and spacecraft guidance.
In general, the physical-quantity sensor includes a physical-quantity sensor element that outputs a sensor signal in response to a physical quantity applied from outside, and a physical-quantity detection circuit that uses a detecting signal for extracting a physical quantity signal from the sensor signal. This physical-quantity sensor may produce an unexpected phase-shift between the sensor signal and the detecting signal due to variations in its manufacturing processes (e.g. diffusion dispersions in resistors or capacitors) or environmental changes (e.g. change in temperature). It is thus required that the phase relation between the sensor signal and the detecting signal be adjusted so as to synchronize the sensor signal to the detecting signal.
In recent years, micro-processing techniques in circuits have been developed, whereby digitization is progressing in the physical-quantity detection circuits. Japanese Patent No. 2728300 (PTL 1) discloses a signal processing circuit for biaxial angular velocity sensor. This circuit is implemented by a digital circuit in which an analog-digital conversion circuit converts a sensor signal supplied from a sensor into a digital sensor signal, a sinewave signal generation circuit for generating a digital sinewave signal, and a digital multiplier for multiplying the digital sensor signal by the digital sinewave signal.
FIG. 13 illustrates a process of the analog-digital conversion circuit in the physical-quantity sensor. The analog-digital conversion circuit samples a sensor signal every sampling period while being synchronized to a sampling clock, and converts analog values (amplitude values) A0, A1, A2, . . . of the sampled sensor signals into digital values P0, P1, P2, . . . .